This invention relates generally to electrical switches and more particularly to switches using spring disc elements which move between opposite convex and concave configurations and which are actuated upon the occurrence of selected conditions such as pressure or temperature.
Conventional condition responsive switches have a contact arm movable between first and second switch positions prebiased to one switch position and have a dished snap acting disc element movable between opposite convex and concave configurations for moving the switch between switch positions in response to the occurrence of selected temperature or pressure conditions. Such switches are intended to perform selected control functions in response to the occurrence of the selected temperature or pressure conditions in a zone to be monitored. An example of a switch of this type is shown and described in U.S. Pat. No. 4,581,509 which issued to the assignee of the present invention.
This type of switch has become widely used, among other applications, in automotive environments such as in the air conditioning refrigeration compressor systems. For example there is a need in such a system to provide a switch to protect the system from excessive high pressure. Additionally, there is a need to provide a switch to protect the system from a loss of freon and lubricant charge and resulting compressor damage. Both of these switches are connected to operate the compressor clutch either directly or through a computer control system. Both switches are typically mounted in the compressor housing and communicate with the high pressure side of the system. The high pressure protection device typically opens on pressure increase to about 430 psi while the high side low pressure switch typically closes on pressure increase to 50 psi.
It is an object of the present invention to provide apparatus which provides both of the above functions in a single housing. Another object of the invention is the provision of a switch apparatus for dual functions which employs fewer parts than prior art switches and which also saves on installation cost and space required for such installation.
Briefly, in accordance with the invention a normally open electric switch is mounted adjacent first and second vertically aligned discs adapted to move from one dished configuration to an opposite dished configuration upon the occurrence of selected conditions. According to a feature of the invention the first disc is disposed in a first disc receiving chamber and has a normally concave surface configuration facing the switch. The first disc has a centrally disposed aperture through which a motion transfer pin extends between a movable contact arm of the electric switch and the second disc disposed in a second disc receiving chamber. The second disc has a normally convex surface configuration facing toward the switch and is mounted in a pressure-force converter which is adapted to move the second disc toward a reaction surface. A motion transfer member is placed between the two discs. The first disc is adapted to invert its curvature upon being exposed to increasing pressures of a selected first level or above, and the second disc is adapted to invert its curvature upon being exposed to increasing pressures of a selected second, higher level or above. At pressures below the first level, the first disc prevents actuation of the switch and at pressures above the second level the second disc allows deactuation of the switch.
Alternative embodiments use a floating ring to transfer motion between the discs and provides a reaction surface for the second disc.
Another embodiment disposes the first and second discs in direct engagement with one another.